1. Field of the Invention
The present invention relates to an electronic device and more particularly to an electronic device capable of decreasing the power consumption (stand-by power) while not in operation (not in use).
2. Description of the Prior Art
Conventional electronic devices will now be described by way of VTRs for example. Most of VTRs have a timer recording function, and usually because of the necessity of performing the timer recording, a primary power supply circuit is kept ON and part of a secondary power supply circuit remains connected thereto, even in the state of power OFF (including a timer recording stand-by state).
Therefore, even with the second power supply circuit OFF (including a timer recording stand-by state), electric power is supplied continually to the primary power supply circuit, that is, electric power continues to be consumed, which corresponds to a power consumption of several watts or so even while not in use (not in operation).
A power control system circuit in such a VTR, as shown in FIG. 9 which is a circuit diagram of principal portions, substantially comprises a primary power supply circuit 1 to which AC 100V is fed through a terminal 1a, a power transformer 2, a signal and motor system power circuit 3 and a control system power circuit 4 both serving as secondary power supply circuits, a signal and motor system circuit 6, a control system circuit 7 constituted of a microcomputer, a power control transistor 8, a resistor 9, a switching transistor 10, and an ON/OFF switch 11 which provides a switching signal between start-up state and stand-by state.
When electric power is fed to the power control system circuit and the power supply of the electronic device is ON, the switch 11 is turned OFF by an operator or a shift to a timer recording stand-by mode is instructed by an inputting operation, the control system circuit 7 detects this state and sends a signal to the power control transistor 8 to turn OFF the transistor, whereby the switching transistor 10 is turned OFF and the supply of electric power from the signal and motor system power circuit 3 to the signal and motor system circuit 6 is cut off, so that the electronic device is turned OFF.
In the conventional electronic device, even with power OFF, the signal and motor system power circuit 3 and the control system power circuit 4 both constituting the secondary power supply circuit are connected to the primary power supply circuit 1 to which AC 100V is inputted through the power transformer 2, thus giving rise to the problem that the consumption of power is continued as a stand-by power.
For solving this problem there has been proposed an electronic device in which a relay is connected to the primary power supply circuit 1, though not shown. In such an electronic device with a relay connected to the primary power supply circuit, the control system circuit 7, on detecting an ON/OFF operation of the switch 11, turns ON or OFF a relay driving transistor (not shown), thereby turning the relay ON or OFF, whereby the primary power supply circuit 1 can be turned ON or OFF.
In such a conventional electronic device, however, in the event a malfunction such as runaway should occur in the control system circuit 7 for some reason or other, it becomes impossible for the control system circuit 7 to detect the operation of the switch 11 even if the switch is operated ON or OFF and thus it becomes impossible to control the ON/OFF operation of the relay. If the primary power supply circuit 1 is ON in such a case, there is a fear that an excessive current may flow in the power control circuit.
Since the interior of the aforesaid relay is hermetically sealed, it has been impossible to operate the relay manually from the exterior. Therefore, in the event the control system circuit 7 should become uncontrollable as mentioned above, the user had no choice but to pull out the terminal la from the associated plug receptacle to stop the supply of electric power to the primary power supply circuit 1 in order to ensure safety.
At ordinary homes, however, an electronic device such as TV or VTR is in many cases disposed in close proximity to a wall of a room, and a plug receptacle for insertion therein of the terminal 1a is wired in the wall. For pulling out the terminal 1a from the plug receptacle it is necessary to move the electronic device disposed in close proximity to the wall, which movement is difficult for a powerless person.